Method and system for explicit ap-to-ap sounding in an 802.11 network

ABSTRACT

A method of one AP accessing a channel occupied by a neighboring AP within CCA range, by acquiring channel knowledge via performing cooperative sounding and setting a null towards the neighboring AP, under certain conditions verifications, is provided herein. The method may include: transmitting and receive signals via a plurality of radio circuitries connected to plurality of antennas; monitoring signals received by the radio circuitries and generating a list of neighboring co-channel access points that each has plurality of antennas and are further located within a clear channel assessment (CCA) range of the access point; and instructing the radio circuitries to transmit a sounding sequence to the list of neighboring access points, and receive Channel State Information (CSI).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/449,431 filed on Aug. 1, 2014, which claimsbenefit from U.S. Provisional Patent Application Ser. No. 61/955,433filed on Mar. 19, 2014, all of which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to wireless communication, andmore specifically to high efficiency Wi-Fi.

BACKGROUND OF THE INVENTION

Prior to setting forth the background of the invention, it may behelpful to set forth definitions of certain terms that will be usedhereinafter.

The term “Wi-Fi” as used herein is defined as any wireless local areanetwork (WLAN) products that are based on the Institute of Electricaland Electronics Engineers (IEEE) 802.11 standards.

The term “Access Point” or “AP” as used herein is defined as a devicethat allows wireless devices (also known as User Equipment or “UE”) toconnect to a wired network using Wi-Fi, or related standards. The APusually connects to a router (via a wired network) as a standalonedevice, but it can also be an integral component of the router itself.

The term “client” as used herein is defined as any device that haswireless communication capabilities, specifically, the IEEE 802.11standards. A client may be for example a smart telephone, a laptop, atablet or a personal computer (PC).

The notation “STA” as used herein is defined in as an IEEE 802.11client.

The term “BSS” is an acronym for Basic Service Set, which is typically acluster of stations supported by an AP.

The term “node” as used herein is defined as general name for both IEEE802.11 AP and IEEE 802.11 STA.

The term “serving AP” as used herein is defined in relation to one APand one STA, wherein the STA is registered to the AP, and the AP and STAare sending and receiving data to and from each other.

The term “neighboring APs” or “neighboring nodes” relate to twoco-frequency (or co-channel) APs or nodes that are within each other'ssensitivity range, e.g. at least one of them can receive the other insuch an signal-to-noise ratio to allows decoding of signals.

The term “CCA range” as used herein is a range between two IEEE 802.11nodes, wherein at least one node can receive the other's transmission ata power level equal or larger than “CCA Level” e.g. −82 dBm.

The term “CSMA/CA” stands forCarrier-Sense-Multiple-Access/Collision-Avoidance, representing arequirement to listen before transmitting in a multi-node wirelesssystem that shares a common channel on the basis offirst-come-first-served.

The term “preamble” as used herein describes a certain 802.11transmitted signal modulation appearing at the beginning of each packet,that when received by other 802.11 nodes, will force them to yieldchannel access.

The notation “SINR” stands for Signal to Interference and Noise.

The term “ACK” as used herein, stands for acknowledgement, and isdefined as the signal transmitted from an IEEE 802.11 receiving node tothe IEEE 802.11 node that has transmitted a packet to it, provided thepacket was successfully received.

The term “time division duplex” (TDD) as used herein refers to systemsusing the same frequency spectrum for methods of communications in atime division manner such as Wi-Fi systems.

The term “channel sounding” as used herein refers to the process definedin 802.11 specifications that enables the full dimensionality of theradio channel to be determined. One sounding technique described in the802.11 specifications is for an AP to transmit a Null Data Packet (NDP),a packet without a MAC frame.

The term “implicit feedback” or “implicit sounding” as used hereinrefers to a process used for TDD protocols such as Wi-Fi, where bothdown and up links share the same spectrum. In the aforementionedprocess, the uplink channel estimated by the AP, is assumed to beidentical to the downlink one—based on reciprocity principle—and istherefore is considered by the AP to represent the channel towards theclient/STA.

The term “explicit AP-STA feedback” or “explicit sounding” as usedherein refers to a procedure where AP transmissions are channelestimated by the STA, and then fed back to the AP, providing it with themagnitude of phase and amplitude differences between the signals astransmitted by the AP vis-à-vis as received by the client/STA, allowingit to gauge possible distortions and correct them.

The term “associated STA” as used herein refers to a STA that is servedby a certain AP with a certain Service Set Identifier (SSID).

The term “non-associated STA” as used herein refers to a STA within therange of the non-serving AP.

The acronym “NAV” stands for Network-Allocation-Vector and representsvirtual carrier sense mechanism, used by a Wi-Fi transmitting message tobroadcast the predicted duration of its transmission, signaling to othernodes how long the channel will be occupied.

The acronym “RTS” stands for Request-To-Send, and represents a messagetransmitted by one Wi-Fi node to another, probing it for informationabout its availability to receive data, per the Wi-Fi Alliance protocol.

The acronym “CTS” stands for Clear-To-Send, and represents a positiveresponse from the other node to the node originating the RTS, indicatingto the requesting node that the channel is clear from its point of viewas well.

The notation “DURATION” is a message embedded in both RTS and CTS,representing a prediction of the future traffic about to be transmittedbetween two nodes that have captured the channel; other nodes thatreceive it, must clear the channel as long as the DURATION has notexpired; other nodes that have received the RTS but received the CTS(hidden nodes) will avoid accessing the channel, allowing the receivingnode to successfully complete the reception.

The acronym “FLA” stands for Fast Link Adaptation, and representsprocesses that reduce transmitting side learning time of the receiver'sSINR.

The acronym “MCS” stands for Modulation Coding Scheme, mapping SINR tomodulation order and code rate.

The term “beamformer” as used herein relates to a node that generates aspatial pattern, created by two or more antennas, formed in such a waythat significantly in the power level received by a given receiver beinga “beamformee”.

The term “null” as used herein, is a spatial pattern, created by two ormore antennas, formed in such a way that significantly reduces the powerlevel received by a given receiver (e.g., a local minimum). An “Rx Null”is a null formed by a receiver's antennas weight in order to decreaseundesired signal level. A “Tx Null” is formed by transmitter's antennasweights in order to decrease its undesired transmitted signal at remotereceiver's input.

The term “actual null depth” as used herein, is the estimated value ofthe null after a certain time period has elapse since the last explicitsounding in which the amplitude and the phase have drifted so as toyield null degradation. The actual null depth is the original nulltaking account the estimated null degradation.

APSS is an acronym for AP Sounding Set. This is a cluster of APs thatwork together with mutual sounding process to reduce interferenceaccording to this invention.

The term “AP Beacon” is a management signal that is transmitted atregular intervals (typically about 10 times per second) that indicatescapability of the AP. The Beacon frame contains both mandatoryinformation (such as SSID) and optional data that may include vendorspecific information. This vendor specific data field is used toindicate the AP as an APSS capable.

AP* indicates an AP which is compatible with APSS, meaning it isequipped with special software so that it can participate in APSS,either as a sounder or as a responder.

AP*_1 indicated an AP that initiates the APSS process. If multiple AP*are present, then multiple APSS's exist.

APSS_ID indicated an N bit random code selected by AP*_1 to identify theAPSS that it has created (e.g. N=12).

AP*_i indicates an AP member in a group of APs that is a recipient of anAP*_1's initiation of an APSS process, where I {2 . . . n} is thedesignator for the different AP* that are members of the APSS_ID. Alsolabeled as “Compatible Access Point”.

According to current IEEE 802.11 air protocols, two neighboring APs candownload traffic (e.g. radio signals including data) over the samefrequency channel to their respective STAs at the same time as long asthese APs are not within CCA range of each other. When an RTS/CTSprocedure is used, an additional condition is introduced. Namely, alegacy STA receiving the download traffic from its serving AP, must notbe within CCA range of other neighboring APs or the STA they aresupporting, if the AP is occupying the channel.

In many deployments APs on the same radio channel are within CCA rangeof each other; thus, an AP may be blocked from transmitting to itsclient STA due to activity of a neighboring nearby AP.

SUMMARY OF THE INVENTION

Embodiments of the present invention disclose a protocol modificationthat allows a group of 802.11 nodes that are MIMO capable, to access anoccupied channel, using novel procedure that enables acquiring knowledgeof the channel between APs, based on setting up an explicitbeamformer-beamformee handshake.

According to some embodiments, an AP equipped with Tx/RX MIMO capabilitymay serve several STAs while simultaneously null its transmitted signaltoward the interfering AP, based on acquiring channel knowledge via asounding process targeted at neighboring APs, similar to explicitsounding process defined for 802.11ac beamforming and MU-MIMO targetedat served STAs.

Embodiments of a MU-MIMO procedure are described herein, enabling aneighboring AP to access a channel already occupied by anotherdownloading AP; the procedure may be initiated by establishing asubgroup of neighboring APs which agree to adhere to a mutual soundingprotocol, e.g. subscribe to an AP Sounding Set (APSS), exchanginginvites and accepts to the set, and performing mutual soundinghandshakes that enable acquisition of each other's channel information,consequently used for null setting towards each other—also labeled asbeamformer-beamformee nulling process.

Each of the aforementioned member AP may perform an APSS initializationby surveying the neighboring co-channel APs periodically, listing thosewho are within its CCA range, and eliminating from the list ones thatare not APSS capable, and ones that are too strong to be nulled, e.g.,ones that cannot be pushed below CCA Level via nulling, either due tolimited nulling capability, or due to a very close proximity, or both.

The aforementioned beamformer's nulling capability is defined as thepower level difference between its trained null towards the Beamformee,and its Omni directional antenna pattern, as received by theBeamformee's receiver.

Such nulling capability is estimated by a beamformer AP via periodicalsounding of the APs that are within its CAA range, and by theninterpolating the acquired phase and amplitude accuracy deteriorationover time, which has elapsed from last sounding.

Successful nulling capability verification may allow a beamformer AP toaccess (for downloading purposes) a channel occupied by the downloadingbeamformee AP, provided certain additional conditions are met.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best bemore fully understood by reference to the following detailed descriptionwhen read with the accompanying drawings in which:

FIG. 1A is a block diagram illustrating a typical operationalenvironment in accordance with the prior art;

FIG. 1B is a block diagram illustrating an access point with transmitand receive MIMO capability;

FIG. 2 is a block diagram illustrating an example of the effect of usingnulling in accordance with some embodiments of the present invention;

FIG. 3 is an initialization phase in accordance with some embodiments ofthe present invention;

FIG. 4 is an example of APSS message flow in accordance with someembodiments of the present invention;

FIG. 5 is an APSS sounding announcement in accordance with someembodiments of the present invention;

FIG. 6 is an APSS Null Data Package in accordance with some embodimentsof the present invention;

FIG. 7 is an APSS feedback in accordance with some embodiments of thepresent invention;

FIG. 8A is a flow chart for an AP serving a single STA at a given time(SU-MIMO) in accordance with some embodiments of the present invention;

FIG. 8B is a flow chart for an AP serving multiple simultaneous STAs(MU-MIMO) in accordance with some embodiments of the present invention;

FIG. 9 is an example of fading gradient in accordance with someembodiments of the present invention;

FIG. 10 is a null deterioration chart as a function of phase andamplitude imbalance, in accordance with some embodiments of the presentinvention; and

FIG. 11 shows the structure of the Beacon frame, where APSS capabilityis indicated in the optional vendor specific portion of the frame inaccordance with some embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, various aspects of the present inventionwill be described. For purposes of explanation, specific configurationsand details are set forth in order to provide a thorough understandingof the present invention. However, it will also be apparent to oneskilled in the art that the present invention may be practiced withoutthe specific details presented herein. Furthermore, well-known featuresmay be omitted or simplified in order not to obscure the presentinvention.

Unless specifically stated otherwise, as apparent from the followingdiscussions, it is appreciated that throughout the specificationdiscussions utilizing terms such as “processing,” “computing,”“calculating,” “determining,” or the like, refer to the action and/orprocesses of a computer or computing system, or similar electroniccomputing device, that manipulates and/or transforms data represented asphysical, such as electronic, quantities within the computing system'sregisters and/or memories into other data similarly represented asphysical quantities within the computing system's memories, registers orother such information storage, transmission or display devices.

FIG. 1A is an apparatus illustrating an area covered by two accesspoints in accordance with the prior art. AP_1 101 is assumed to beequipped with an omni directional antenna pattern 105, that schedulesdownloading a packet to one of its served Stations STA_1 102, and isblocked by its previously set NAV or DURATION invoked by a neighboringAP_2 103 which has already seized the channel.

The reason for the protocol's requirement that prohibits AP_1 fromtransmitting is to avoid harmful interference to the AP_2's session, aswell as in consideration of a possible harmful interference of AP_2transmission to AP_1's contemplated package delivery.

It is noted that in cases depicted in FIG. 1A, such mutual harmfulinterference are not likely to affect the success of actual downlinkreception by the respective STAs, being out of range; however, AP_1 101access to the channel is prohibited in order to guarantee the ACK 110response from STA_2 104 will not be jammed. Specifically, in the exampleof FIG. 1A AP_1's 101 harmful interference 109 toward AP_2 103, may jamSTA_2 ACK 110 reception by AP_2's receiver resulting in a need forretransmission.

FIG. 1B is a block diagram illustrating an AP 110 within CCA range of aneighboring AP 103, in accordance with some embodiments of the presentinvention. AP 110 may include for example a plurality of antennas 10-1to 10-N, a plurality of radio circuitries 20-1 to 20-N configured totransmit and receive signals via a plurality of antennas 10-1 to 10-N incompliance with the IEEE 802.11 standard, and a baseband processor 30.AP 110 may be configured to transmit and receive signals within a clearchannel assessment (CCA) range of neighboring AP 103 which has aplurality of antennas and may be configured to transmit and receivesignals in a co-channel shared with AP 110 in compliance with the IEEE802.11 standard.

Baseband processor 30 may be configured to monitor signals received bythe radio circuitries 20-1 to 20-N and generate a set or list ofneighboring co-channel access points that each has plurality of antennasand are further located within a clear channel assessment (CCA) range ofthe access point. Baseband processor 30 may be further configured toinstruct radio circuitries 20-1 to 20-N to transmit a sounding sequenceto the list of neighboring access points, and receive Channel StateInformation (CSI) therefrom. The sounding sequence being a sequence ofcontrol frames sent to beamformees and data frames indicative of thechannel from the beamformee.

FIG. 2 is a block diagram in which the baseband processor may further beconfigured to set weights on the radio circuitries to produce a null atone or more receiving antennas of the listed neighboring access pointwhich currently transmits on the same frequency channel. The FIG. 2layout describes an apparatus that is similar to the one illustrated inFIG. 1A, but with APs equipped with features according to embodiments ofthe present invention labeled AP*_1 201 and AP*_2 203 respectively.These features may allow an AP to use another AP's busy channel undercertain conditions. Embodiments of the present invention are based onAP*_1 201 driving a null on both the receive and the transmit paths,towards AP*_2 203, thus protecting both of their ACK receptions, 207 and210, from each other's transmissions. When AP*_1 Omni radiation pattern205 is replaced by novel radiation pattern 212 in both up and downlinks, then both 208 and 209 harmful interference signals are reduced.When such a reduction is estimated by AP*_1 201 to reach a level thatallows both ACK 210 and ACK 207 to be successfully received, and whenother conditions described below are met, then AP*_1 201 may proceed todownload a packet to STA_1 202, while AP*_2 203 is downloading itspacket to STA_2 204. It is noted that the aforementioned nulling isbased on cooperative process between the participating APs which belongto the same AP Sounding Set (APSS), as will be detailed herein.

According to some embodiments, an explicit sounding process invokedbetween the access point and each of the listed neighboring accesspoints.

FIG. 3 is a flowchart illustrating a high level process according toembodiments of the invention of inviting and accepting of soundinginvitations between APs that are equipped with the aforementionedcooperative nulling capability, committing to respond to soundingrequests from other set members. Embodiments of the process 300 startwith scanning all neighboring APs that are APSS compatible and arewithin CCA range 301. Then, a list up to 8 strongest RSSI's (or adifferent number) is generated 301-B. Then the first AP*_i from the listis being picked from the list 302. AP*_1 then sends Request-to-Join-APSSto the picked AP*_i 303. An AP*_i which receives a Request-to-join, mayrespond with ACK-to-APSS, or alternatively, may not respond; in oneembodiment, such a decision is based on limiting the response to theimmediate neighboring AP*_i which project the most interference, forexample limit to 4 APs with the strongest RSSI.

In a case that AP*_1 receives any ACK-to-APSS response 304, AP*_1updates its APSS table 305. In a case AP*_1 does not receive anyACK-to-APSS response, the next AP*_i from the list is being picked andthe method goes on to the AP*_1 sending Request-to-Join-APSS to thepicked AP*_i 303 and so forth. When a Request-to-Join is not beingresponded with ACK-to-APSS, AP*_i may re-send the Request-to-Joinseveral times, (e.g. resending the Request-to-Join three times, eachrequest being sent a few milliseconds after the previous request) beforeproceeding to next neighboring AP*_i 306, and revisit the non-respondingAP*_i after an extended time period, e.g. 1 minute.

One embodiment of the invention has APSS compatible AP indicate theircapability by a flag set in a vendor specific information element (forexample Element Identifier (ID) 122) in the beacon management frame (Seee.g. FIG. 11), in which case only APSS capable APs within CCA range areprobed with a Request-to-Join-APSS (AP Sounding Set) 303. APs that arewithin reception range may elect to respond with ACK-to-APSS 304; APsthat elect to respond are doing it with a ACK-to-APSS 304, and then timestamping and RSSI are logged per BSSID 305 as outlined in table 307 ofthe figure.

Once the list of APSS is established, each AP*_i can try to access anoccupied channel following the APSS procedure which is based onexpanding the 802.11ac multi-user-MIMO (MU_MIMO) explicit sounding.

In essence, the APSS process in one embodiment differs from the existingMU-MIMO by replacing one of the simultaneously served STAs with aneighboring AP; specifically, an AP that is capable of serving Lsimultaneous STAs, is configured to serve only L−1 STAs while nulling aneighboring AP which is currently occupying the channel.

FIG. 4 is a diagram illustrating protocol sequence enabling embodimentsof the present invention. Specifically, APs that adhere to APSS requireair protocol modifications that support AP to AP explicit sounding asdescribed in the invention. In the example shown, and similarly toMU-MIMO (IEEE 802.11ac), AP*_1 issues an NDP Announcement to several APsin APSS. As opposed to MU-MIMO, one of these nodes is not a client STA,but rather a given AP*_i. As shown in the example, the first to respondis the AP*_2, and following are polling and responses towards and fromAP*_3's, and subsequently to AP*_4. In another embodiment, this ordermay be altered.

According to some embodiments of the present invention, beamformer AP*_1may send an NDP announcement to the listed neighboring beamformees APs,followed by an NDP, and a compressed matrix V representing the channelresponse (herein: compressed V response) from a first neighboring AP*_iand a series of poll requests to a next beamformee neighboring AP*_i anda corresponding V compressed response, until all listed neighboringbeamformees neighboring APs are polled and all V compressed responsesare consummated.

FIG. 5 is a timing diagram 500 illustrating a modification of theMU-MIMO protocol in the NDP announcement field 505, facilitating an APSSmessaging in accordance with embodiments of the present invention. TheNDP announcement exhibits an identical structure to 802.11 AC NDPannouncement with following changes: APSSID contains the APSS ID that isestablished when APSS is established while other fields have identicalrole to 802.11AC sounding.

More specifically, the two byte STA field 506 of the MU-MIMO protocol isretrofitted into a APSS ID field 501, rather than a STA field,containing similar structure, i.e. a subfield APSS ID (e.g. 12 bits), asubfield indicating the FB feedback type being used (e.g. 1 bit), and asubfield NC the Number of Columns in the feedback matrix (e.g. 3 bits).

According to some embodiments of the present invention, the APSS NDPannouncement and NDP may include an APSS ID field replacing in the MUMIMO protocol the STA ID field.

FIG. 6 is a timing diagram 600 illustrating the MU-MIMO protocol. NDP602 according the MU-MIMO protocol is shown here in detail illustratingthat the APSS process remains unchanged and specifically it is identicalto the MU-MIMO corresponding field of IEEE 802.11ac. By way ofnon-limiting example, assuming a 4 antenna AP, operating in 40 MHzbandwidth, there would be 4 VHT-LTF sub-frames, with 6 symbols persub-frames for 96 μsec as illustrated herein.

FIG. 7 is a timing diagram 700 illustrating a breakdown of the PollRequest field 702. According to some embodiments of the presentinvention, the Poll Request field may be retrofitted (e.g., used for adifferent purpose without altering the basic structure of the protocoland its fields) to address neighboring beamformees APs rather than STAsin the MU MIMO protocol. Specifically, fields 704 and 706 that wereoriginally reserved for STAs in the MU-MIMO protocol are now reservedfor APs.

There is a set of topologic conditions and qualifications that areverified before an AP*_1 may perform an APSS process and access the busychannel: the beamformer AP is outside the CCA range of the STA currentlyserved by the beamformee AP; the beamformee AP is outside the CCA rangeof the STA to be served by the Beamformer AP; both served STAs areverified to be located closer than the edge of their serving cells,since their corresponding AP*'s' sensitivity is slightly reduced byminor residual interference caused by the APSS process conditions areoutlined as follows:

-   -   Beamformer AP identifies the Beamformee served station by        decoding the destination field, and either does not identify        such a STA MAC address in its neighborhood, or receives it at        RSSI<CCA level;    -   Beamformer AP identifies the MCS transmitted by the Beamformee        AP to its served STA, and uses it in order to calculate the        proximity of said STA to the Beamformee's cell edge, e.g. low        MCS may indicate large range, and if so, will refrain from        accessing the channel;    -   The beamformer AP will use RTS/CTS for serving the STA it is        intending to download data to, in order to make sure said STA        will not be jammed by the beamformee AP; and    -   The beamformer AP will gauge the RSSI of the CTS coming from the        STA it is intending to serve, calculates the proximity of the        STA to the beamformer AP's cell edge, in which case it will        refrain from accessing the channel.

Additionally, in order to guarantee the AP*_i session is not harmed bythe AP*_1 access, a null depth verification and validation is required.

FIGS. 8A and 8B outline the sequence for a Single User MIMO (SU-MIMO)service with nulling of a neighboring AP, and a Multi User MIMO(MU-MIMO) service with nulling of a neighboring AP, respectively,according to embodiments of the present invention. Within the first fewmicroseconds of the APSS process, phase and amplitude informationaccuracy are considered virtually perfect, and capable of yielding avery deep null (e.g. better than 30 dB).

FIG. 8A illustrates flowchart 800A for SU-MIMO mode. In step 801-a AP*_1has data for STA_x. In step 802-a the AP*_1 NAV is checked whether it isset or not. In a case that the NAV is set, in step 803-a it is checkedwhether the nulling capability of AP*_1 is sufficient to guarantee noharm to AP*_i current session. In a case it is sufficient, in step 805-athe NAV is ignored and the nulling process proceeds to step 806-a forsetting up a null towards AP*_i and further to step 807-a to sendingdata to STA_x. In a case that AP*_1 NAV is not set, the process goes ondirectly to step 807-a to sending data to STA_x. In a case that thenulling capability of AP*_1 is insufficient to guarantee no harm toAP*_i current session, the process goes on to step 804-a to waiting forthe NAV to clear before sending data to STA_x.

FIG. 8B illustrates flowchart 800B for MU-MIMO mode. In step 801-b AP*_1has data for STAs_x, y, and z. In step 802-b the AP*_1 NAV is checkedwhether it is set or not. In a case that the NAV is set, in step 803-bit is checked whether the nulling capability of AP*_1 is sufficient toguarantee no harm to AP*_i current session. In case it is sufficient, instep 805-b the NAV is ignored and the nulling process proceeds to step806-b for setting up a null towards AP*_i and further to step 807-b tosending data to STAs_x, y, and z. In a case that AP*_1 NAV is not set,the process goes on directly to step 807-b to sending data to STAs_x, y,and z. In a case that the nulling capability of AP*_1 is insufficient toguarantee no harm to AP*_i current session, the process goes on to step804-b to waiting for the NAV to clear before sending data to STAs_x, y,and z.

As a non-zero time has elapsed between such last APSS channel estimationand the usage of the acquired weights for nulling, a null deteriorationestimation is performed as described below, and then a nullingcapability is calculated as described further, yielding actual nulldepth figure of merit Null_(—depth).

Therefore, proceeding to AP*_1 access of the occupied channel, isconditioned by measuring RSSI_(AP*) _(—) _(i) of the AP*_i as receivedby AP*_1, and verifying that RSSI_(AP*) _(—) _(i)−Null_(—depth)<CCALevel (e.g. −82 dBm), or another agreed upon dynamically calculated CCALevel.

According to some embodiments of the present invention, a decision toaccess a channel occupied by a listed compatible neighboring AP withinCCA range, may be subject to verification and validation of the accesspoint null's capability to reduce the interference caused by the accesspoint to the neighboring AP below CCA Level, for at least one of theneighboring AP antennas.

According to some embodiments of the present invention, the access pointmay be configured to keep or store records (e.g. on a memory) of fadingrates of each listed compatible neighboring APs within CCA range, interms of amplitude and phase variation over time, and further calculatesfor each of the listed neighboring APs the standard deviation 1σ, 2σ, 3σof the amplitude and phase variations, and further estimates acorresponding amplitude and phase drift rate.

According to some embodiments of the present invention, the access pointmay be further configured to keep or store records of fading rates ofeach listed compatible neighboring APs within CCA range, in terms ofamplitude and phase variation over time, and further calculates for eachof the listed compatible neighboring AP within CCA range the standarddeviation 1σ, 2σ, 3σ of the amplitude and phase variations, and furtherestimates a corresponding amplitude and phase drift rate.

According to some embodiments of the present invention, the access pointmay be further configured to estimate the nulling capability bycalculating the time elapsed between the last sounding of the compatibleneighboring AP within CCA range and the time the condition is beingexamined, apply the amplitude and phase drift rate, and furtherestimates the null depth degradation, caused by the accumulated drift,yielding actual null depth.

According to some embodiments of the present invention, the access pointmay be further configured to null compatible neighboring AP within CCArange while downloading a packet to served STA, in a case where theneighboring AP RSSI—Actual Null Depth<CCA Level, provided severalpredefined topologic conditions are met.

According to some embodiments of the present invention, the topologicconditions may be defined as, for example: (i) the access point is notwithin CCA range of the STA served by compatible neighboring AP withinCCA range (ii); the neighboring AP is not within CCA range of the STA orSTAs about to be served by the access point (iii); and/or the servedSTAs are not on their servicing cell's edges.

AP*_1 may perform periodical APSS sounding process with a given AP*_i,when the AP*_i is not transmitting; such period are preferably done atintervals larger than the maximum packet duration (e.g. 7 ms or more).

According to some embodiments of the present invention, the access pointmay perform the sounding of the listed neighbors that have agreed tojoin the APSS, on a periodic basis, whenever a given compatibleneighboring AP within CCA range is not transmitting. Such periods arepreferably carried out at intervals longer than the maximum packetduration (e.g. 7 ms or more).

According to some embodiments of the present invention, the access pointmay be configured to limit a number of responses produced by it so as toallocate up to approximately 10% of a transmitting time to respond tosounding requests from the listed neighboring access points.

According to some embodiments of the present invention, the sounding ofthe listed neighboring access points may be performed based on IEEE802.11ac MU MIMO sounding procedure, wherein the access point mayrespond to a limited number of compatible neighboring APs including upto eight strongest RSSIs.

According to some embodiments of the present invention, the access pointmay carry out an actual download of a packet to a STA, or a group ofSTAs, while the channel may be occupied by a compatible neighboring APwithin CCA range, may be carried out with such antenna pattern that mayminimize the power received by at least one of the neighboring APantennas.

Following fading fluctuation over time, and average time intervalbetween consecutive APSS sounding, a phase and amplitude gradients arecalculated (e.g. standard deviation 1σ, 2σ, 3σ), and applied to a nulldeterioration chart (See FIG. 10), yielding null depth figure of merit.

FIG. 9 is a diagram 900 illustrating AP*_1 assessment process of fading,according to embodiments of the present invention, based on loggingphase and amplitude differences between pairs of antennas, anddetermining fluctuations over time. Transmitter 902 being an AP*_1transmits a fading channel 905 to receiver AP*_i 904. Fluctuations areshown over time in a phase diagram 906 and amplitude diagram 908. In oneembodiment, such fluctuations are calculated as peak-to-peak phasechanges over 5, 10, 20 and 50 ms wherein the largest 10 percent are notconsidered (e.g. within two standard deviations 2σ), yielding possibleaccumulated phase and amplitude errors.

FIG. 10 is a graph diagram 1000 illustrating an example of resultantcalculations applied to calculation formula that estimates a nulldeterioration in dB (vertical axis) versus phase and amplitude settinginaccuracy in degrees (horizontal axis), the different lines indicatedifferent gains in dB. When applying phase and amplitude imbalance, aneffective or actual null depth is derived, and then a nulling capabilityis verified as follows: RSSI_(AP*) _(—) _(i)−Null_(—Depth) must in someembodiments be lower than allowed CCA Level, in order to allow AP_* 1 toproceed to accessing the busy channel.

FIG. 11 is a diagram illustrating the structure of the 802.11 BeaconFrame 1100 in accordance with embodiments of the present invention. Thisframe is transmitted by all 801.11 APs at a periodic rate, typically 10times per second. This beacon includes mandatory information such as theSSID of the AP but can optionally include other information, e.g. vendorspecific data. Typically the vendor specific data may start with adevice/vendor ID followed by a flag to indicate APSS capability. WhereAPSS becomes standardized, a specific Information Element ID could beassigned to indicate capability rather than embedding this informationin a vendor specific data element.

According to some embodiments of the present invention, the access pointmay include: a plurality of antennas; a plurality of radio circuitriesconfigured to transmit and receive signals via the plurality ofantennas; and a baseband processor configured to monitor signalsreceived by the radio circuitries and generate a list of neighboringco-channel access points that each has plurality of antennas and arefurther located within a clear channel assessment (CCA) range of theaccess point.

The baseband processor may further be configured to instruct the radiocircuitries to transmit a sounding sequence to the list of compatibleneighboring access points, and receive Channel State Information (CSI)from the compatible neighboring access points, wherein the compatibleneighboring access points indicate having a capability of responding tosounding sequences by transmitting identification of the capability in abeacon management frame. The baseband configuration capabilities may bebroadcasted to the compatible neighboring access points via unused bitswithin the beacon management frame.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or an apparatus.Accordingly, aspects of the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” For example, abaseband processor or other processor may be configured to carry outmethods of the present invention by for example executing code orsoftware.

The aforementioned flowcharts and block diagrams illustrate thearchitecture, functionality, and operation of possible implementationsof systems and methods according to various embodiments of the presentinvention. In this regard, each block in the flowchart or block diagramsmay represent a module, segment, or portion of code, which comprises oneor more executable instructions for implementing the specified logicalfunction(s). It should also be noted that, in some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

In the above description, an embodiment is an example or implementationof the inventions. The various appearances of “one embodiment,” “anembodiment” or “some embodiments” do not necessarily all refer to thesame embodiments.

Although various features of the invention may be described in thecontext of a single embodiment, the features may also be providedseparately or in any suitable combination. Conversely, although theinvention may be described herein in the context of separate embodimentsfor clarity, the invention may also be implemented in a singleembodiment.

Reference in the specification to “some embodiments”, “an embodiment”,“one embodiment” or “other embodiments” means that a particular feature,structure, or characteristic described in connection with theembodiments is included in at least some embodiments, but notnecessarily all embodiments, of the inventions. It will further berecognized that the aspects of the invention described hereinabove maybe combined or otherwise coexist in embodiments of the invention.

The principles and uses of the teachings of the present invention may bebetter understood with reference to the accompanying description,figures and examples.

It is to be understood that the details set forth herein do not construea limitation to an application of the invention.

Furthermore, it is to be understood that the invention can be carriedout or practiced in various ways and that the invention can beimplemented in embodiments other than the ones outlined in thedescription above.

It is to be understood that the terms “including”, “comprising”,“consisting” and grammatical variants thereof do not preclude theaddition of one or more components, features, steps, or integers orgroups thereof and that the terms are to be construed as specifyingcomponents, features, steps or integers.

If the specification or claims refer to “an additional” element, thatdoes not preclude there being more than one of the additional element.It is to be understood that where the specification states that acomponent, feature, structure, or characteristic “may”, “might”, “can”or “could” be included, that particular component, feature, structure,or characteristic is not required to be included.

Where applicable, although state diagrams, flow diagrams or both may beused to describe embodiments, the invention is not limited to thosediagrams or to the corresponding descriptions. For example, flow neednot move through each illustrated box or state, or in exactly the sameorder as illustrated and described. The descriptions, examples, methodsand materials presented in the claims and the specification are not tobe construed as limiting but rather as illustrative only.

Meanings of technical and scientific terms used herein are to becommonly understood as by one of ordinary skill in the art to which theinvention belongs, unless otherwise defined.

The present invention may be implemented in the testing or practice withmethods and materials equivalent or similar to those described herein.While the invention has been described with respect to a limited numberof embodiments, these should not be construed as limitations on thescope of the invention, but rather as exemplifications of some of thepreferred embodiments. Other possible variations, modifications, andapplications are also within the scope of the invention. Accordingly,the scope of the invention should not be limited by what has thus farbeen described, but by the appended claims and their legal equivalents.

1. An access point (AP) comprising: a plurality of antennas; a pluralityof radio circuitries configured to transmit and receive signals via theplurality of antennas; and a baseband processor configured to monitorthe signals received by the radio circuitries and generates a list ofneighboring co-channel access points (APs), each is further locatedwithin a clear channel assessment (CCA) range of said access point,wherein the baseband processor is further configured to establish asubgroup of neighboring co-channel APs which agree to join an accesspoint sounding set (APSS), instruct the radio circuitries to transmit asounding sequence to said APSS, and receive channel state information(CSI) therefrom.
 2. The access point according to claim 1, wherein thebaseband processor is further configured to set weights on the radiocircuitries to produce a null at one or more antennas of said APSS whichcurrently transmits on a same frequency channel and download a packet toa station (STA), or a group of STAs.
 3. The access point according toclaim 2, wherein the null weights are determined via explicit soundingprocess invoked between said access point and each of the APSS, based onAPSS Null Data Packet (NDP) announcement by said AP and response byAPSS.
 4. The access point according to claim 3, wherein the AP sends anAPSS NDP announcement to all APs in APSS, followed by an NDP, and a Vcompressed response from a first neighboring AP and a series of pollrequests to a next neighboring AP and a corresponding V compressedresponse, until all APs in APSS are polled and all V compressedresponses are consummated, wherein V is a compressed matrix representingthe channel response.
 5. The access point according to claim 3, whereinthe APSS NDP announcement and NDP comprise an APSS ID field replacing inthe IEEE 802.11ac MU MIMO sounding protocol the STA ID field.
 6. Theaccess point according to claim 3, wherein the Poll Request field isretrofitted to address a neighboring APs rather than STAs in the IEEE802.11ac MU MIMO sounding protocol.
 7. A method of performing anexplicit sounding process to neighboring access points (APs) by abeamformer access point (AP) comprising: transmitting and receivingsignals via a plurality of radio circuitries connected to a plurality ofantennas; monitoring the signals received by the radio circuitries andgenerating a list of neighboring co-channel access points, each beinglocated within a clear channel assessment (CCA) range of the accesspoint; establishing a subgroup of neighboring co-channel APs which agreeto join an access point sounding set (APSS); and instructing the radiocircuitries to transmit a sounding sequence to the list of neighboringco-channel access points, and receive channel state information (CSI)from APs in APSS.
 8. The method according to claim 7, wherein thebaseband processor is further configured to set weights on the radiocircuitries to produce a null at one or more antennas of said APSS whichcurrently transmits on a same frequency channel and download a packet toa station (STA), or a group of STAs.
 9. The method according to claim 8,wherein the null weights are determined via explicit sounding processinvoked between said access point and each of the APSS, based on APSSNull Data Packet (NDP) announcement by said AP and response by APSS. 10.The method according to claim 9, wherein the AP sends an APSS NDPannouncement to all APs in APSS, followed by an NDP, and a V compressedresponse from a first neighboring AP and a series of poll requests to anext neighboring AP and a corresponding V compressed response, until allAPs in APSS are polled and all V compressed responses are consummated,wherein V is a compressed matrix representing the channel response. 11.The method according to claim 9, wherein the APSS NDP announcement andNDP comprise an APSS ID field replacing in the IEEE 802.11ac MU MIMOsounding protocol the STA ID field.
 12. The method according to claim 9,wherein the Poll Request field is retrofitted to address a neighboringAPs rather than STAs in the IEEE 802.11ac MU MIMO sounding protocol.